Today, I have just finished evaluating Kester's EM907 (SAC305)lead free solder paste and found that for our applications it performs as expected. End result that I am encouraged with the results that we got. The equipment that I used:

An SMT2020 to paste the assembly. I found that the paste had a light chemical smell, but not offensive to our SMT staff. The paste was mixed prior to spreading onto the stencil. The paste rolled well and we found that the characteristics were close to the reported specifications on the data sheet. The SMT operators commented that they liked this paste because it didn't stick to the squeegee.

Stencil apetures were reduced 90%. We found that it will be of importance to have the deposited paste 100% on the pads. Through reflow the paste did not completely spread on the pads and passive components did not self center as well.

Pick and place was done with a Mydata TP9-2U. We found that there was no change in performance.

Reflow was with a Heller 1500 5 zone oven. With this assembly a 5 zone will be fine due to the assembly technology and thermal mass. The assembly was a two layer pcb. Components were mostly 0805's, 1206's, MELF's and SO8's. The components were tin/lead. The PCB measured 11"X18" with some ground plane with a tin/lead immersion on the pads.

Inspection was with a microscope at upto X10. Pad coverage was the 90% of the stencil, not complete but acceptable for our applications. I found that the solder joints were well formed, with only a slight dullness as compared with a tin/lead joint. The solder joints were significantly more shiney that other pastes.

Four profiles were created, the first being my upper control limit and the last being the lower control limit.

Next step is taking pictures of the joints for our lead free assembly quality manual.

All in all I am encouraged by my results and wanted to share some good news with the community. I've been studing and planning for lead free in electronics since late 1999 and I must say it is nice to be able to be hands on.

Thanks for the info! I have found that we see similar if not the same results. It appears that lead free processing through SMT is NO BIG DEAL. You will find that other paste Mfgrs seem to have the same performance as what you experienced.

The company I work for (equipment supplier) ran some tests with lead free material in air and N2 environements for reflow. In the air reflow environement it was noticed that the material does not spread, much like you found in your studies. The solder joint was strong, looked good, etc.. but the centering and spreading of the material was poor. Once N2 was used in reflow then the material spread much better to cover the whole pad and centering was a bit better but no impact to the actual solder joint.

From what I have been researching air reflow works just fine with most lead free materials. I have seen more lead free stenicls go to a 1 : 1 relationship on pad to stencil apetures due to the lack of spreading in air reflow. Of course this brings in other issues like extra wiping, gasketing, etc..

Sure, to be a true lead free enviroment all components need to be lead free or fall within the specifications of lead free as defined by the RoHS Directive. What I am doing is starting stage 1 of our journey. Layed out it looks some thing like this. Stage 1: Convert SMT to lead free Stage 2: Convert wave solder to lead free Stage 3: Convert PCB's to lead free Stage 4: Purchase lead free components when available Looking at the entire journey can be daunting, however if it is done one part at a time, It is much easier to digest.

Tom, has your company started to convert your BOMS? How is your company doing it?

Yes, I think that is on most peoples minds, how to do the BOM conversions is the main worry, and I think that it just boggs some companies down so they dont do anything. For us we will take the approach of bringing the lead free parts in as new part numbers and gradually changing over our boms through our ECN process as we get new lead free parts in. They may be used as a subsitute, in reality the primary, but by going this route we may not have to roll part numbers so many times. Currently the thinking is to start burning off our lead parts now and in parralel to stages 1-3, start stage 4. I believe the easier part will be the profiles and the mechanical aspect of going to lead free. Currently our offshore PCB vendors have some lead free processes to offer. We chose to go with Tin immersion, as it seems the most process friendly and the most cost friendly. Thought was given to tin whiskers, but I feel that we will not have products in the tempature where they form. Amazing as it sounds, our primary component vendor has been working aggresively on locating and bringing in lead free parts for us.

Jay, Yes, we did assigned new part numbers for our lead free components. Our concern was how do we know that this component is lead free. New part numbers was our only way. It made the component engineers cry, but offer them a box of Krispy Kreames and work it out with them.

We choose Immersion Silver as a board finish as well. Finish selection is a touchy subject to many and maybe should be a whole new thread.

Your findings looked much inline with what we found. You sound like you have done your homework and thats great! Many people have yet to develop anything more then a written plan on how they would implement if they decided to go lead free. As you know, there isn't any manual out there to give you step by step instructions. If anything, the more you dig into it, the more questions will be raised.

I'm curious, is your company planning to switch over to lead free 100%? If so, is it going to be a sudden change or gradual?

Hi Tom, Thanks for the compliment. I've been researching and planning for the time that my company would go lead free since late in 1999. I hear you there, how do we know that the component is lead free. Baring a leap of faith with your vendors, I think we may have our incoming inspection use a chemical swab that tests for lead on the components. This does incure an additional cost, but the last thing I would want is to get nixed out of the EU because our vendor shipped us lead parts by mistake. My company to the best of my knowledge is going to switch over gradually. If all goes well we will be 100% lead free by the deadline. I'm pretty sure the EU will push it out some, BUT I'm not gooing to take the chance. By gradually transitioning to lead free we can burn up old stock and gradually bring in lead free components as they become available. I know that there are pro's and con's for this route, but I feel that it is the best way for us. In the next week, I'll be profiling one of our most thermally dense assemblies, I'm looking forward to this. I think that it will bring a lot of confidence to the owners and CEO, that this process will work. Tom, do you have wave solder up and running lead free yet? For my machine (Electrovert econopak 1) There is a lead free upgrade, but it is good only for 1-3 years before it needs to be replaced. Currently My thought is to go Titanium or have my pumps and nozzles coated with ceramic.

Ther is a solder alloy out there that is supposed to allow lead free wave processing without having to upgrade pumps and such or increasing the pot temp (direct drop in). I have not used it nor do I plan on doing leadfree wave soldering but you may want to give them a call about it.

P.S. We also had all P/Ns changed to reflect leadfree vs. lead. One thing to look at is you are probably already seeing leadfree components and don't even know it. I just noticed today that we received some reels from Kemet of a Tant cap and noticed that they are now labeled lead free. We did not order lead free but that is what we received, I am going to try and find out if we will ever receive pb parts from them again so we can determine if these particular P/Ns need to be changed for pbfree or if we can leave them as they are since they are now lead free.

Concerning you PCB, what TG do you expect to use for your lead free process?

On my side I have a problem. I order PCB from Canada and from China. My PCB vendor in china is producing a lot of OSP and ENIG PCB, no HASL lead free and in Canada they will produce HASL lead-free. Is someone have a suggestion concerning this problem.

I have two 5 zones reflow and I don't have any problem to get the lead-free profil and the result is not as good as Sn/Pb but it's almost the same. It's much better than what I've heard in seminars.

I looked breafly at this alloy. My concern was that I had already implemented a SAC 305 alloy at SMT. So any of my mixed technology projects would one alloy (SAC 305) on one side (topside) and a different alloy (SN100C) on the bottomside. Most articles I have read state that you need to use the same alloy for reworking/touch up of a solder that the original solder joint was made. This would result in carrying 2 different wire solder alloys. Then requiring the operators to know and remember which side they are working on. Operators are operators and to ask them this would be too difficult. I'm curious, any users of the SN100C out there? If so, what are your findings?

Hi Frank, we're still going to go with FR4 as our prefered material. Our board thickness is .062. We use an on shore and off shore vendor. Prototron I believe offers an immersion tin and excellence in china? offers an immersion tin finish. We found that the immersion tin was only 10-15% above what we were paying. My thoughts is that this price will come down as they get more requests for this process. Cocerning SN100C wave soldering, I am going to a Seminar concerning this mix. Its in Redmond washington. If any one is interested here is the link for registration. http://www.ftcassembly.com/seminars.htm I'm interested in finding out what they have to say about sn100c. I also have a 5 zone oven and don't think the profiling or results are as bad as what I've heard. I think with any thing new the doom sayers come out of the wood work. Best regards, Jay Brower

Jay - I read your report and was interested to see that you ran your evaluation on a Heller 1500 5 zone. We have been hearing for some time that a larger machine (7 zone min)with higher temp heaters and fan motors would be required. Is yours a "hi temp" oven? Any comments here relative to reflow equipment? Scott

Hi Jay, please let us know your inputs from the seminar regarding SN100 Nihon solder from FCT. This solder seems to have a higher melting temp of 221C. It prints well and visually looks similar to SAC alloy. Have no reliabilty data though.

Indy, I found the same findings as you. The claim is that the solder joint may actually look closer to a SnPb solder joint then the SAC alloys. I had commited to the SAC alloys at SMT before finding out about the SN100C alloy. I'm interested in what Jay finds out as well.

To be able to use current wave solder machine with out the costly retros or new purchases would be a great. As far as reliabilty data, it may be some what limited because it is a patented alloy and thus not as popular as some of the SAC alloys.

Hi Scott, My Heller is a bog standard Heller 1500 with an edge guide. There is nothing special about it. I would of course love to have a 7 zone oven, but...I have to use what is here at this time. My only concern with a 5 zone oven is the change in tempature that the small chips go through I've been able to achieve about a 3C degree delta. I'd rather be under 2.5degrees/sec. so as to not crak or damage components. One thing to note is that My machine is in a fairly well regulated enviroment with a relatively stable ambient temp. I think however in a shop that does not have either air conditioning or a way to deal with changes in tempature, a 7 zone might be better. I've been hearing the same thing also..."You must have a 7 zone oven!" My 5 zone will probably be fine for the assemblies that we do. Maybe down the road I'll be able to invest in a 7 or 8 zone oven. Also To my understanding, that with a proper moisture control policy for smt components; components that are relatively moisture free can deal with the hotter temps and changes better. One thought that we have is to use some sort of dessicant cabinent if needed. Jay

Hi Tom, I did talk to Bob Gilbert about the sn100c. His comment is that it is a nickle stabalized alloy. Simplisticly, the tin and copper molecules would rather bond with the nickle. He also mentioned that with the SAC alloys, the manufactuers were adding alot of phosphorous todecrease the amount of dross generation, and this addition of phosphorous acts to wet the stainless steel in the wave nozzles and pumps. I believe that there will still be some amount of deterioration of the solder pot, but how moch I have no idea, there may be none at all. Bob indicated that there are reports done, and they should be on there web site soon. I'll be more than happy to write up what I find on Thursday. Jay

I found the previous discussion of lead free profiles on 5 zone ovens very interesting. I had the same concerns, but have recently succeeded in creating profiles on a 5 Zone QUAD oven that have eliminated solder splatter or Solder on Gold with Leaded Paste and Lead Free paste. The same results have been achieved on 7, 10 zone convection ovens as well as 4 zone Conceptronics 60 ovens with ~2.5 degree C/sec rates. The more zones the better, but it can be done providing the ovens are working properly. However the boards I have been working with are realitively simple assemblies, in otherwords they do not have extreme component variaties or high heat sinking devices. They do have caps, rnets, soics, and FBGAs.

Jay ~ do you have any other contact information for that seminar you are attending concerning the SN100C? I have tried the URL in your message, and it is not working for me. Your help would be much appreciated, and thanks for sharing all your helpful info. Sara

I have the same Heller 1500 and am about to start evaluating paste. Would you be so kind as to provide your oven set points to give me a baseline to start with? I think this would save myself and others a lot of time and effort ;-)

The directive is called RoHS. Meaning that is not only the lead that is the issue. The materials need to whithstand a hihger temperature, not only delta T is an issue (but huge). Moisture sensitive devices: how to handle these? You will see an increase of moisture sensitive level for some compents. There must also be a plan for of how to handle the packages that have been open for a certain time; let say that a machine breaks down... How many times can you bake a component? What surface protection on the pcb:s; gloves needed? Shelf life on the pcb:s? Bom's? Etc. etc. etc.

I must say that it is a real challenging, but if we see it in this point of view: under the past 100 years, mankind has somewhat destroyed the earh, so we all have a responsibility for the next generation to pass on... What was it Armstrong said: it's a small step for a man but a huge...

This is the profile we came up with on a 1500 to satisfy the parameters suggested by Indium. This was on an FR4 1mm thick 4 layer pcb that I would descrbe as medium density, QFP, SOP, AL-CAP, TANTS, D-PAK, MINI SPRING COIL, SOT and CHIPS were all used with no apparent damage - though I am still waiting for functional test which will probably not happen until next year. Wetting on ENIG was very good from what I have seen of other Pb-free assemblies. Three thermocouples used. 1 on bottom in the open, 2 on QFP lead, 3 on top in the open. 120 to 217 93.5 to 103 seconds Total above 217 65 to 76 seconds Peak 230.4 to 240.2 Maximum rising slope between 120 to 217 = 1.5 seconds Cooling rate with no forced cooling from peak to 150 was 2.5 seconds Settings are 90, 140, 200, 250,255 for both top and bottom Conveyor at 45cm/min.

Could you expand on the results you observed about improved wetting in a nitrogen environment? I am very interested to learn about the impact that nitrogen had. Was there an improvement in the cooling zone with nitrogen?

> The directive is called RoHS. Meaning that is > not only the lead that is the issue. The > materials need to whithstand a hihger > temperature, not only delta T is an issue (but > huge). Moisture sensitive devices: how to handle > these? You will see an increase of moisture > sensitive level for some compents. There must > also be a plan for of how to handle the packages > that have been open for a certain time; let say > that a machine breaks down... How many times can > you bake a component? What surface protection on > the pcb:s; gloves needed? Shelf life on the > pcb:s? Bom's? Etc. etc. etc. > > I must say that > it is a real challenging, but if we see it in > this point of view: under the past 100 years, > mankind has somewhat destroyed the earh, so we > all have a responsibility for the next generation > to pass on... What was it Armstrong said: it's a > small step for a man but a huge...

Yes, there are many factor and challenges to this ROHS. For more information, please visit http://www.lead-freetest.com, there are free resource and usefully link that help you to understand.